Circuit protector

ABSTRACT

A circuit protector including an electromagnetic device, said device comprising a coil through which circuit current flows and wound on a coil bobbin, a cylinder provided at the center of said bobbin, an oil-dash type plunger provided within said cylinder movably against a compression force of a spring arranged between a cylinder head and the plunger, a yoke integrally connected to said cylinder and the bobbin, and an armature mounted to an end of said yoke in a manner capable of being attracted to the plunger head, said bobbin is provided with a magnetic leakage in the vicinity to the cylinder head.

United States Patent Setone et al.

[ Sept. 5, 1972 [54] CIRCUIT PROTECTOR [72] Inventors: Isami Setone,Seto; Akira Yoshino,

Owari Asahi, both of Japan [73] Assignee: Matsushita Electric Works,Ltd., Primary Examiner-Harold Broome Osaka, Japan Attorney-W0lfe,Hubbard, Leydig, Voit & Osann [22] Filed: April 22, 1971 ABSTRACT [21]Appl' 136,416 A circuit rotector includin an 'electroma netic P g 8device, said device comprising a coil through which [30] ForeignApplication Priority Data circuit current flows and wound on a coilbobbin, a

cylinder provided at the center of said bobbin, an oil- Apnl 27, 1970Japan ..45/36138 dash yp plunger provided within said cylinder movablyagainst a compression force of a spring ar- (g1 3356;251:5352 rangedbetween a cylinder head and the plunger a y integrally connected to Saidcylinder and the [58] Field of Search ..335/63, 62, 61, 236 bobbin, andan armature mounted to an end of said yoke in a manner capable of beingattracted to the [56] Refimces Cited plunger head, said bobbin isprovided with a magnetic UNITED STATES PATENTS leakage in the vicinityto the cylinder head. r

3,517,357 6/1970 Bakes ..335/63 4 Claims, 7 Drawing Figures 9 I I I c 7E] ;l O

CIRCUIT PROTECTOR This invention relates to a circuit protector.

In general, the transformer or solenoid allows such a great overcurrentas 1,500 3,000 percent of rating current to flow temporarily at thestarting moment. In a convention circuit breakers or protectors,therefore, there has been such a drawback that the electromagnet deviceis actuated actuated by electromagnetic force produced only in the coilbefore the plunger moves due to the attraction and, thus, the circuitbreaker itself is apt to operate before such overcurrent reaches stableregion (or the starting current disappers).

The present invention has been proposed to remove the above drawback andis so constructed that the circuit protector is not actuated by thestarting current but actuated by the overcurrent continuously flowingduring operation by increasing magnetic leakage so as to increaseattracting ampare turn of the armature and by minimizing the leakage atthe time of completion of attraction of the plunger, so that the aboveproblem will be effectively solved.

It is a principal object of the present invention to provide a circuitprotector which is not actuated by any temporary overcurrent flowing atthe starting moment but actuated by a continuous current flowing duringthe operation.

Other objects and advantage of the present invention will become clearas the following descriptions set forth with reference to theaccompanying drawings, in which;

FIGS. 1A and 1B show the electromagnet device for use in the circuitprotector according to the present invention and, in particular, FIG. 1Ais a longitudinal cross section of the device and FIG. 1B is a crosssectional view taken along the line I I of FIG. 1A;

FIG. 2 is a partially sectioned elevation of the circuit protectoraccording to the present invention, in which the electromagnet device ofFIG. 1 is utilized;

FIG. 3 is an equivalent circuit; and

FIGS. 4 to 6 are explanatory diagrams for explaining the characteristicsof the present device as compared with the conventional one.

FIGS. 1A and 1B show respectively only electromagnet devices to be usedin the circuit protector according to the present invention, and FIG. 1Ais a sectional elevation and FIG. 1B is a sectional side view takenalong the line I I of FIG. 1A.

To begin with, explanation will be made of the structure and operationof the electromagnet with reference to FIGS. 1A and 1B.

In the drawings, a coil 1 is wound around a bobbin 2 made of insulationmaterial within which a cylinder 3 made of nonmagnetic materials such asbrass is disposed. A plunger 4 is slidably arranged within the cylinder3 with an oil filled therein. A plunger head 5 made of magnetic materialis provided at the head portion of the cylinder 3. A compression spring6 is arranged so as to engage between the plunger head 5 and aprojection extending from the front face of the plunger 4. The bobbin 2is fixed to an L-shaped yoke 7 provided with an upper flange 9 and sideflanges 8, through the latter of which the cylinder 3 penetrates. 10 isa pair of upstanding bent portions of the yoke 7, with the electromagnetdevide is secured to an insulative housing. 11 and 11 are leakagemagnetic paths arranged in the vicinity to the plunger head 5 and atopposite sides with respect to the cylinder 3 as inserted in a flange ofthe bobbin 2. The upper ends of the leakage magnetic paths 11 and 1 1'are connected to the yoke 7. An armature 12 is located in front of theplunger head 5 and is pivoted to the insulation housing 14 (See FIG. 2)at the upper portion thereof by'means of a shaft 15. Another compressionspring 13 is disposed between the armature 12 and the bobbin flange 8 atthe armature side.

FIG. 2 illustrates an example of the circuit protector embodying theelectromagnet device as shown in FIGS. 1A and 1B. The armature 12 isrotatably secured through the shaft 15 to the housing 14 made ofinsulating material. A hook 16 is rotatably coupled to the armature 12at the shaft 15 and the right end of a seesaw type turning plate 17 isengageably provided above the hook 16. The left end of the turning plate17 is kept in contact with a sliding member 18 which slides up and down.Slidably secured to a downward leg 19 of the sliding member 18 is amovable contactor 20. 21 is a fixed contactor secured to the insulationhousing 14 below the movable contactor 20. 22 indicates a spring engagedbetween the movable contactor 20 and the fixed contactor 21. 23 is apush button. 24 is a link, the upper end of which is rotatably securedto the push button 23 through a pin 27 and the lower end of which isalso rotatably secured to the turning plate 17 through a pin 26. 25indicates a testing rod. With the structure as above mentioned, upondepression of the push button 23, resulting force is transmitted to theturning plate 17 through the link 24, thereby the pin 26 pivoting theplate 17 is descended along a slot 26 provided on the insulation housing14. The right end of the turning plate 17 comes into contact with thetop portion of the hook l6 and the left end depresses the sliding member18 downward and, therefore, the movable contactor 20 comes into contactwith the fixed contactor 21. In this case, the pin 27 engaged to thelower portion of the push button 23 is likewise descended along an L-shaped slot 27' in the housing 14 and locked in its sideward bottom portand, thus, the contacts are maintained in their ON state. When the lowerpart of the armature 12 is attracted toward the plunger head 5 in thedirection of an arrow as shown by a steady state overcurrent flowingthrough the coil 1, the top portion of the armature 12 rotates clockwiseand in turn the top portion of the hook 16 also rotates clockwise and isreleased from engagement with the right end of the turning plate 17. Asa result, the movable contactor 20 is urged upward by the force of thespring 22 and thus the contacts reach OFF state. Depression of thetesting rod 25 rotates the top portion of the armature l2 clockwise andthe contacts are opened in the similar manner to the foregoing.

Next, the operation of the device according to the present inventionwill be described in detail.

When the plunger 4 is positioned away from the plunger head 5, thelowering of magnetomotive force between the plunger 4 and the plungerhead 5 will become large due to a large leakage magnetic flux caused bythe leakage circuits l1 and 11 and, therefore, effective magnetomotiveforce for the armature 12 through the distance of the attraction gap gis small. For this reason, the armature does not actuate with thetemporary overcurrent.

When the steady state overcurrent flows through the coil 1 and theplunger 4 moves inside the cylinder 3 to contact with the plunger head5, the magnetomotive force with the attraction gap 3 to the armature 12does not greatly differ from the magnetomotive force afforded to thecoil 1, if the leakage at the part of the plunger 4 and the yoke 7 andthe saturation of the iron core are made as small as possible, even whenleakage magnetic flux of the leakage circuits 11 and 1 1' is large in acertain extent. When the overcurrent flows through the coil 1 in thissteady state, the armature 12 is attracted by attractive force producedby this overcurrent, thereby the contacts are opened.

FIG. 3 shows an electric equivalent circuit in which the followingreferences are used:

F: Magnetomotive force applied to the coil.

Rp: Magnetic reluctance of the plunger and the plunger head.

Re: Magnetic reluctance of the leakage circuit.

Ra: Magnetic reluctance of the attraction gap of the armature.

r: Magnetic reluctance of the yoke, plunger and their connectingportion.

In FIG. 3, if Rp becomes zero,fa F r(a+ e). With Re provided, fa isreduced only by the item r-rbe and, if r is reduced, fa does not differfrom the case where Re is not provided, as far as Rp is small. Namely,in the steady state where the plunger is close to the plunger head, fais determined independently of Re and the armature normally operateswith the overcurrent, thereby the contacts are opened.

When Rp is great, e-Rp will be large and fa becomes considerably smalleras compared with the case where Re is not provided. That is, in thiscase, fa is small due to Re and the armature does not actuate with theovercurrent, so that the contacts remain in closed condition.

FIG. 4 is a characteristic diagram showing the variation of the armaturemagnetic flux rim with respect to the change in plunger position, i.e.,in the distance between the plunger and the plunger head, wherein curveA represents the case having no leakage circuit and curve B representsthe case having the leakage circuit.

FIG. is a characteristic diagram showing the variation in the attractiveforce to which the armature is subjected with magnetomotive force fa,with respect to the armature gap, i.e., the change in distance betweenthe armature and the plunger head, in which curves C and D represent thevariations when plunger stroke from the head is zero in the caseswithout and with the leakage circuit, and curves E and F represent thevariations when the stroke is mm. in the cases without and with theleakage circuit.

FIG. 6 is a characteristic diagram, in which the ab scissa indicates thevariation of distance between the plunger and the head and the ordinateindicates magnification of current value at which the circuit protectoroperates with respect to the value of rating current,

in which curve G represents the case without the leakage circuit andcurve H represents the case with the leakage circuit.

As will be seen from these characteristic curves, it is possible toobtain a prptecto having an electromagnetic tripping mechanism 0 a largeinstantaneous opearation value, when the magnetic leakage circuit isprovided in the electromanget device, according to the presentinvention.

According to the present invention, as detailed in the foregoing, thecontacts do not open at the starting current which is temporaryovercurrent not enough to move the plunger 4, while the contacts closewith the overcurrent occurring at the steady state lasting for apredetermined time period.

What is claimed is:

1. An electromagnetic circuit protector comprising the combination of anarmature mounted for pivotal movement between first and second positionsfor opening a pair of electrical contacts to protect an electricalcircuit, a magnetizable pole member located at said second position, amagnetizable plunger mounted for reciprocating movement in anon-magnetizable cylinder leading to said pole member, biasing meansurging said plunger away from said pole member, a magnetizable yokehaving one end located closely adjacent said plunger and a second endextending toward said armature and said pole member, a coil disposedaround said cylinder for advancing said plunger toward said pole memberagainst the urging of said biasing means when the coil is energized fora predetermined time interval, thereby attracting said armature to saidpole member due to a first magnetic circuit formed by said yoke,plunger, pole member and armature, and magnetizable short circuitingmeans contacting said yoke and extending to a position proximate to saidpole member and lying in substantially the same plane as said polemember in the direction transverse to the direction of movement of saidplunger so that the short circuiting means is substantially as far fromsaid plunger as said pole member, said short circuiting meanscooperating with said pole member, yoke and plunger to form a secondmagnetic circuit for short circuiting a part of the magnetic flux fromsaid first magnetic circuit when said plunger is not engaging said polemember and thereby preventing attraction of said armature to said polemember when said coil is energized for only a short time interval lessthan said predetermined time interval.

2. The circuit protector according to claim 1 wherein said coil is woundon a flanged bobbin and said short circuiting means is disposed at bothsides of the pole member in a flange of the coil bobbin.

3. The circuit protector according to claim 1 wherein said pole memberis positioned between the armature and the short circuiting means.

4. The circuit protector according to claim 1 wherein said yoke andarmature are formed in an integral body member.

1. An electromagnetic circuit protector comprising the combination of anarmature mounted for pivotal movement between first and second positionsfor Opening a pair of electrical contacts to protect an electricalcircuit, a magnetizable pole member located at said second position, amagnetizable plunger mounted for reciprocating movement in anon-magnetizable cylinder leading to said pole member, biasing meansurging said plunger away from said pole member, a magnetizable yokehaving one end located closely adjacent said plunger and a second endextending toward said armature and said pole member, a coil disposedaround said cylinder for advancing said plunger toward said pole memberagainst the urging of said biasing means when the coil is energized fora predetermined time interval, thereby attracting said armature to saidpole member due to a first magnetic circuit formed by said yoke,plunger, pole member and armature, and magnetizable short circuitingmeans contacting said yoke and extending to a position proximate to saidpole member and lying in substantially the same plane as said polemember in the direction transverse to the direction of movement of saidplunger so that the short circuiting means is substantially as far fromsaid plunger as said pole member, said short circuiting meanscooperating with said pole member, yoke and plunger to form a secondmagnetic circuit for short circuiting a part of the magnetic flux fromsaid first magnetic circuit when said plunger is not engaging said polemember and thereby preventing attraction of said armature to said polemember when said coil is energized for only a short time interval lessthan said predetermined time interval.
 2. The circuit protectoraccording to claim 1 wherein said coil is wound on a flanged bobbin andsaid short circuiting means is disposed at both sides of the pole memberin a flange of the coil bobbin.
 3. The circuit protector according toclaim 1 wherein said pole member is positioned between the armature andthe short circuiting means.
 4. The circuit protector according to claim1 wherein said yoke and armature are formed in an integral body member.